This application is a U.S. National-Stage application under 35 U.S.C. § 371 of International Application No. PCT/JP2004/001509, having an International Filing Date of 12 Feb. 2004, which claims priority to Japanese Patent Application No. 2003-035665, filed on 13 Feb. 2003, both of which are incorporated by reference herein.
The present invention relates to a method of cutting diamond for providing a diamond with a strong brilliance and diamonds obtained thereby, and more particularly to a method of cutting diamond in which ten, which is considerable number in comparison with conventional diamonds, projections of heart and allow are observed under a predetermined lighting condition.
Conventionally, a diamond comprises a generally trapezoidal conic crown having a flat table on top, a generally conic pavilion having an acute curette, and a strip-like girdle provided on the lateral surface along the boundary of the crown and the pavilion. A conventional diamond is commonly cut in order to form a table 81, eight crown main facets 82, eight star facets, and sixteen upper girdle facets 84 on the crown side and eight pavilion main facets 85 and sixteen lower girdle facets 86 on the pavilion side by a method called ‘round brilliant cut’ as shown in FIGS. 11 and 12.
For applying a polishing process on the pavilion side by the above-mentioned method, for example, one of ridges 91 of raw diamond 3 in crystal form shown in FIGS. 8(a) and 13(a) is flatten and a first pavilion main facet 92 centered on the ridge 91 (refer to FIG. 13(b)) is formed as a first step. Subsequently, three other ridges 91 are flatten in a similar manner as mentioned above and four pavilion main facets 92 are formed altogether as shown in FIG. 13(c). In the event as mentioned above, four first pavilion main facets 92 are formed and therefore each of the central angles 95 of the main facets 92 becomes ninety degrees. Thereafter, the boundary line 93 formed between two adjacent first pavilion main facets is flatten by polishing and eight pavilion main facets 94 centered on the ridges 91 with the central angles of forty five degrees are formed as a second step.
On the other hand, in the event of applying a polishing process on the crown side, a top portion of the raw diamond in crystal form is cut off in order to form a flat table 103 thereon as shown in FIGS. 8(b) and 14(a). A first crown main facet 104 is formed by polishing a portion centered on a ridge 101 in the raw diamond 3 in crystal form flat and three other pavilion main facets 104 are formed subsequently, which totals to four pavilion main facets as a first step (refer to FIGS. 14(b) and 14(c)). In the event as mentioned above, each boundary line 105 of two adjacent first crown main facets 104 meets the next boundary line with an angle 108 of ninety degrees in relation to a center point. Thereafter, eight of second crown main facets 107 having central angles 109 of forty-five degrees are formed by polishing portions centered on the boundary lines 105 as a second step.
Incidentally, a device called tang 54 for holding the raw diamond 3 and a scaif 51 formed of a flat steel plate strewed with diamond powder are used in the polishing process as mentioned above. The raw diamond 3 is held by the tang 54 capable of changing the angle at forty-five degrees and polished by the rotating surface of the scaif 51 as shown in FIG. 10.
And it is empirically known that a heart and allow phenomenon may be observed in a diamond in an excellent proportion among the diamonds processed as mentioned above by using a magnifying device when one of the main facets of the diamond is illuminated by the light colored through a color filter and the remainder are shielded from incident light. The heart and allow phenomenon is one of the strongest selling point as a proof of excellence in brilliance of the diamond. When a diamond finished in round brilliant cut is mounted in a face-up direction (having a table of a crown upward) under a predetermined lighting condition, eight of allow phenomenon 123 projecting over the surface may be observed as shown in FIG. 15. And when the above-mentioned diamond is mounted in a face-down direction (having the table of the crown downward) under a predetermined lighting condition, eight of heart phenomenon 124 projecting over the surface may be observed as shown in FIG. 16.
Generally diamond is colorless but superior to other jewels in its brilliance. And it is understood that the brilliance caused by reflection called ‘brilliancy’, an iris called ‘fire’ for dispersing light like a prism, and flashes called ‘scintillation’. Therefore, diamonds emitting a stronger brilliance are required.